+1 on everything people said about not having the sheets cleated and/or being super fast to uncleat.
If you are going upwind, you can pinch (will slow you down, give rookies a feeling of safety), or (much better) you can ease the sheets slightly while maintaining course or even footing slightly. The boat will dart forward with speed.
If you are going downwind/broad reach, you can get the initial speed, and then bear away slightly. This will reduce the heeling motion, trade it for pressure forward which will speed you up. Quickly move your weight aft. This works well on newer cats, and flat water. Older cats, chop or if the gust is truly abrupt (and the boat has no chance to pick up speed)... will probably result in a pitchpole. If the gust is _very_ sudden, you might not have a say on the matter
If you're in a reach, you can pick. Don't stay in the reach - upwind and downwind are more stable.
One more kink to this - often a severe gust also has a shift. In the bay I sail in, the dominant wind is East, with gusts that come down with a 15 degree anti-clockwise shift. So when I'm sailing N (reach) or NE (upwind), the shifts "pinch themselves", and feel really manageable. If I'm sailing SE (upwind), the gust shifts "aft" and is much harder to control.